The present invention relates to a belt driving system, having a photographic belt and a transcribing belt, provided in a electrophotographic machine.
A known art, for example of an electrophotographic machine, has a flat belt, including a photographic layer or dielectric layer thereon. The flat belt is wound round a plurality of parallel rollers so that the flat belt, instead of a photographic dram, performs as a photographic belt or a transcribing belt for the purpose of making the machine lightweight and compact.
A base material of the flat belt used for the above usage is mostly material of less extension and high strength such as a plastic film and a metal leaf. Thus, elastic deformation of such a belt is low. Accordingly, when that electrophotographic machine has errors such as dimensional errors of components, installing errors of rollers, unbalance of the belt tension, and uneven length of the belt, the belt cannot compensate for those errors by its elasticity. Consequently, the flat belt creeps (moves laterally) to one side in the widthwise direction of the belt when it is running.
However, the above electrophotographic machine requires high accuracy and high resolving power for a clear picture and the creeping of the flat belt should be prevented.
As disclosed in Japanese Patent Publication Gazette Nos. 56-127501 and 59-205052, a flat belt is provided with a guide for preventing creep, and as in No. 57-630347, a flat belt is provided with a restricting member in order to prevent the creep of the flat belt.
As disclosed in the Japanese Utility Model Registration Laying Open Gazette No. 58-110609, one roller having a belt-position sensor as a creep detecting means is provided for adjusting the creep. In that invention, when the belt-position sensor senses creeping of the belt, the creep is adjusted by displacing the end of a creep adjusting roller. And also as disclosed in the Japanese Utility Model Registration Laying Open Gazette No. 64-48457, when the flat belt creeps, a roller is moved in the direction of the rotating shaft and the rotating shaft of the roller is moved by the movement of the roller. Thus, the creep is adjusted by moving the roller in the direction contrary to the creep.
However, in the invention of the above Nos. 56-127501, 59-205052, and 57-60347, since the creep of the flat belt is restricted by an external factor, it may not be applicable in some cases of bad combinations of a flat belt and a roller. That is, a guide or restricting member should be strong if a belt possesses a large biasing force. Also, bending force resistance of the flat belt in the widthwise direction should be large and strength at the end of the belt should be high enough to avoid damages at side ends of the belt. Thus, the thicker the belt, the harder to apply the above embodiment. Moreover, the guide should be positioned accurately and forming the guide particularly in a seamless belt was hard.
Furthermore, in the above inventions in the Nos. 58-110609 and 64-48457, since the belt creep is detected and the belt is backed to the center by a complicated mechanism, the system will be expensive. Also, since extra space is required, the system should be large. That system possesses another disadvantage such that the system is not reliable enough since the number of components is increased due to complicated structure, which means an increased number of causes of trouble.